1. Field of the Invention
The present invention relates to a wire cutting and feeding device for use in a wire bonding apparatus.
2. Prior Art
A conventional wire cutting and feeding device used in a wire bonding apparatus will be described with reference to FIGS. 12 and 13.
An ultrasonic horn 2 is fastened to a Z direction driver 1 which is driven in the Z (vertical) direction by a Z driving means (not shown), and a bonding tool 3 is fastened to the tip end of this ultrasonic horn 2. A wire damper 4 is attached to a damper attachment plate 5 so as to be located at the rear end of the bonding tool 3. A wire 6 which is supplied from a wire spool (not shown) passes through a hole formed in the ultrasonic horn 2, the wire damper 4, and a guide hole formed in the bonding tool 3, thus extending downward from the tip end of the bonding tool 3.
The clamper attachment plate 5 is fastened to an attachment block 7, and this attachment block 7 is fastened to a slide block 8. This slide block 8 is attached to a base plate 9 via a linear guide bearing 10 which is fastened to the base plate 9, so that the slide block 8 is able to slide on the base plate 9. A cam follower 11 is supported on the attachment block 7 so that the cam follower 11 is rotatable. A motor 12 is fastened to the base plate 9, and a cam plate 13 is fastened to the motor shaft of the motor 12. Furthermore, a coil spring 14 is mounted between the attachment block 7 and base plate 9 so that the cam follower 11 is pressed against the cam plate 13. The base plate 9 is fastened to an attachment base 15 which is equipped with a wire cutting and feeding angle adjustment mechanism, and this attachment base 15 is fastened to the Z direction driver 1. Accordingly, when the Z direction driver 1 moves vertically and in the X and Y directions, the entire apparatus also moves vertically and in the X and Y directions together with the Z direction driver 1.
Next, the wire cutting and wire feeding operations will be described. These operations are performed after the wire 6 has been bonded to a lead (second bonding point).
In particular, after the wire 6 has been pressed against the second bonding point and bonded by the bonding tool 3, the wire 6 is clamped by the wire damper 4, and the motor 12 rotates in the forward direction. When the motor 12 rotates in the forward direction, the cam follower 11 follows the dropping profile of the cam plate 13 against the driving force of the coil spring 14, so that the attachment block 7, slide block 8, damper attachment plate 5 and wire damper 4 are lifted upward by a prescribed amount (maximum: 100 microns) in the direction indicated by arrow A, thus causing the wire 6 to be cut from the end portion of the undersurface at the tip of the bonding tool 3. As a result, wire bonding to one pair of bonding points (i. e., a first bonding point on a pad and a second bonding point on a lead) is completed.
Next, in order to bond the wire 6 to the first bonding point of the next pair of bonding points, wire feeding is performed in which the wire 6 is paid out from the undersurface of the tip of the bonding tool 3 by the wire damper 4. In this case, the motor 12 rotates in the opposite direction from that described above so that the cam follower 11, attachment block 7, slide block 8, damper attachment plate 5 and wire damper 4 are pushed downward by a prescribed amount (maximum: 400 microns) in the direction indicated by arrow B (which is the opposite direction from the direction indicated by arrow A) as a result of the rising profile of the cam plate 13. As a result of this operation, the tail length required for bonding to the next first bonding point is caused to extend from the undersurface of the bonding tool 3.
The conventional wire cutting and feeding device as described above is disclosed in, for example, Japanese Patent Application Laid-Open (Kokoku) No. 56-30118, and a conventional wire cutting and wire feeding method described above is disclosed in, for example, Japanese Patent Application Kokoku No. 4-65537.
In the prior art described above, the motor 12 is used as the driving source; accordingly, the size and weight of the apparatus tend to be large. Furthermore, since the coil spring 14 is used in order to insure that the cam follower 11 attached to the attachment block 7 that holds the wire damper 4 will follow the cam plate 13, the apparatus has a characteristically low-frequency vibration. As a result, the mechanical rigidity of the apparatus is weak, and the apparatus tends to vibrate. Moreover, the feeding precision of the wire damper 4 is determined by the rotational angle of the motor 12, i. e., the rotational angle of the cam plate 13, so that it is difficult to obtain a greater precision.